1. Field of the Invention
The present invention relates to a method for operating interface modules, which can be specified as active and/or redundant, in an ATM communications device, in which the interface modules, which can be specified as active and/or redundant, are connected to a central control unit.
2. Description of the Prior Art
In communications devices, in particular communications devices that operate using the asynchronous transfer mode, virtual connections are often established, maintained and terminated via interface modules with the aid of a central control unit. The central control unit is used here, in particulars to transmit control commands to establish and clear virtual connections to the interface modules.
In order to ensure disruption-free operation and to enable rectification of errors in an active interface module, redundant interface modules and/or redundant transmission paths are provided. If one interface module or transmission path fails, the communications link, in particular a virtual connection, is rerouted to a redundant interface module and/or transmission link. Depending on the level of fail-safety required for a communications device or transmission link, it is possible to provide different redundancy structures for the associated interface module. Examples of these are “1+1”, “1:1” and “1:N” interface module redundancy, cf. in particular “IEEE Journal on Selected Areas in Communications”, VOL. 15, No. 5, June 1997, pages 795 to 806.
With a “1+1” redundancy structure, two interface modules are operated in parallel in order for communication signal streams to be transmitted via them redundantly. Of these communication signal streams transmitted redundantly, only one is used for the further processing of the virtual connection.
With “1:1” interface module redundancy, only one of two interface modules is used as the active interface module, with a switchover being made to the remaining redundant interface module only if the active interface module fails.
With “1:N” interface module redundancy, one redundant interface module is additionally provided for a number N of interface modules. If an error occurs in one of the N interface modules, a switchover is then made to the redundant interface module instead.
With “1:N” interface module redundancy, a selector arrangement is usually connected between the interface modules and the external transmission lines; the selector can allocate the individual transmission lines to the N interface modules and the redundant interface module. It should be noted however that if a selector arrangement fails, or in the event of the selector arrangement being consequently exchanged, all transmission lines connected thereto and the connections they carry are interrupted.
In current communications systems, the central control unit transmits control commands solely to the active interface module, and the active interface module communicates the control commands to the redundant interface module using a communications channel. The active interface module is notified of the receipt of the respective control commands by the redundant interface module. In addition, the active interface module notifies the central control unit of receipt of the control commands only once the control commands have been acknowledged by the redundant interface module. As a consequence, each control command is processed twice by the active interface module during connection establishment or clearing, resulting in a considerable additional dynamic load on the interface module.
An object of the present invention therefore, is to reduce the dynamic load of interface modules, which can be specified as active and/or redundant, in an ATM communications device.